Discussion of units in the MEASUREMENTS class

[michpro]

I have started to analyse the MEASUREMENTS class and would like to propose some modifications in the defined units:

• Type=13 (0x0D) - Energy; I would add electron volts [eV] maybe from outside the SI but still used in physics,
• Type=14 (0x0E) - Power; As an optional unit we have ‘Horse power’ defined, but here there is some ambiguity because there are metric and imperial HPs, and unfortunately they are not equal. 1 [HP (met)] = 735.49875 [W] and 1 [HP (imp)] = 745.69987 [W]. So I think it would be appropriate to define both as optional units. Very occasionally there is still such a 'curiosity' as [erg/s], but since it comes from the deprecated CGS system of measures I would not add it.

[grodansparadis]

Great!

I have added this is the measurement class database Noticed that Wh was missing from the docs for Type=13. Also fixed. eV added. Changed the conversions for horsepower and added imperial.

The working of this is explained here There is many conversions between units still to do.

[michpro]

kWh is duplicated and 'k' should be lowercase :) => 'Optional unit: KWh (1) Optional unit: KWh (2) Optional unit: eV (electron volts) (3)'

[michpro]

Type=32 (0x20) - Speed; We have miles per hour (mph) but are missing the nautical unit 'knot' (international nautical mile per hour [1 kt = 1 INM/h])
By the way: I don't think I'd put the mile and nautical mile into units of length (Type=2 (0x02) - Length/Distance) or their square into units of area (Type=52 (0x34) - Area).

[grodansparadis]

Added knot. Why not adding mile and nautical mile ?

Units and there conversion to unit 0 is here. It is possible add exotic units on idx 4 and above for max 256 variants.

[michpro]

In addition to the mile (imperial and nautical), one would have to add the kilometer,... in this way we will exhaust all resources for the definition of CLASS 1,.... and what to do with an inch if we add miles? And since imperial units are 'curious' then an inch does not convert to full miles in any way.... and then some Anglo-Saxon will come and ask why there is no Furlong here :) ... and will still want to have the speed expressed in Furlongs for two weeks :)

[michpro]

Suggestion: rearrange optional units for Type=28 (0x1C) - Volume.
We have defined “Default unit: cubic meter (m³) Opt. unit: Liter (dm³) (1), decilitre (100 cm³) (2), centilitre (10 cm³) (3), millilitre (cm³) (4)”. Since we can only have 4 units defined for CLASS 1 events, I would leave: “Default unit: cubic meter (m³) Opt. unit: Liter (dm³) (1), millilitre (cm³) (2)”. These two intermediates (100 cm³), and (10 cm³), are not generally used, unlike millilitre (cm³), which is now missing from CLASS 1 events. Sliding units can be left in CLASS 2, but from CLASS 1 I would definitely get rid of them.

[grodansparadis]

Breaking changes like this I seldom accept. But this is a good argument. Changed.

[michpro]

Tesla unit should be marked with a capital 'T' and not 'B'. In addition, placing it in the 'Magnetic Field Strength' category is ambiguous and should not be there. This could have resulted from calling this unit 'magnetic B-field strength', but this 'B' was missing and is not equivalent to the A/m(also denoted H) unit. Tesla is 'Magnetic Flux Density' or 'Magnetic Induction'. The unit 'B' is 'magnetic field magnitude' and can also be expressed in Tesla but => B = μ0I/(2πr) where μ0 = 4π*10-7 N/A2.
In general, with this magnetic field is the same problems :)

[grodansparadis]

10/20 - This should be Oersted, a typo.

See here

[michpro]

Type=33 (0x21) - Acceleration: In description is: 'Meters per second/second (m/s2)' and I think it should be: 'Metre per second squared (m/s²)'. Use the tag for square

[grodansparadis]

Changed

[michpro]

Type=42 (0x2A) - Electric elastance: In description is: 'daraf (f-1)' and I think it should be: 'daraf (F^-1) [inverse farad]'

[grodansparadis]

Fixed

[michpro]

Type=52 (0x34) - Area: I'm thinking of filling in the entire set of CLASS 1, by adding the metric derivatives used to express the area of the territory:

• 1 are = 100 m²;
• 1 hectare = 100 ares = 10000 m² = 0.01 km²;
• 1 km²

[grodansparadis]

The only problem I see here is nothing for micro/nano areas. But add as of your suggestion. There are probably twenty more that can be added here as it seems... :)

[michpro]

Nowhere is there a decibel (dB) unit [Bel(B) itself is probably too large and very rarely used],... the problem is that it's a relative unit, so I don't know whether to put it in Type=58 (0x3A) - Sound pressure (acoustic pressure), or create an additional type.

[michpro]

... in CLASS1.DATA :) ... I also see dBV there, but I don't see dBu :)

[grodansparadis]

What would a new type be named to cover this?

[michpro]

You can use unicode characters to express powers in units: ⁻¹ ² ³ · ... will look better and be more readable

[grodansparadis]

Eventually also units and optional unit will be set from the XML file so I don't put a lot of effort in the hard version. Unicode is used there. Welcomes a pull request that fix it if you feel for it... :)